Prepare the homemade pimento cheese:
Blend the cheddar, mayonnaise, onion, pimentos, garlic and hot sauce in a food processor
until well combined. Transfer the pimento
cheese to a glass jar or bowl and refrigerate
until firm, at least 1 hour. Makes 1¾ cups.

Prepare the burgers: Blend the ground sirloin and
ground short ribs and sprinkle with salt and pepper.
Loosely form the meat into 4 equal 4-ounce patties
about ½ inch thick. Create a small well in the center of each beef patty, using your thumb.

Heat 2 tablespoons of the oil in a small sauté pan
over medium heat. Cook the onions, sprinkling with
salt and stirring occasionally, until caramelized,
brown and soft, 25 to 30 minutes.

Season beef patties with salt and pepper to taste.
Heat a large cast-iron skillet or griddle pan over high
heat and add 1 to 2 tablespoons of the oil. Cook the
burgers, well side up first, until browned on both
sides, 3 to 4 minutes per side. Transfer to a plate.

Spread the homemade pimento cheese on the
non-buttered side of each slice of bread. Top half
of the bread slices with a pile of onions, then add
the burger patties and top with the remaining
bread slices.

Place the sandwiches on the griddle and toast until
the bread is golden brown and the cheese is beginning to melt, 2 minutes per side. Serves 4.